CBSE · Class 12 · Chemistry · Chapter 6

Haloalkanes and Haloarenes — Formula Sheet

Board Formulas

11 formulas

1.SN2 Rate Law (Bimolecular Substitution)★
$Rate = k [R-X] [Nu^{-}]$
$k$ : Second-order rate constant (L mol⁻¹ s⁻¹) · $[R - X]$ : Substrate concentration · $[Nu^{-}]$ : Nucleophile concentration
Second-order overall. Concerted single-step mechanism with a transition state — no intermediate.
2.SN1 Rate Law (Unimolecular Substitution)★
$Rate = k [R-X]$
First-order overall. Two-step mechanism via carbocation intermediate. Independent of [Nu⁻].
3.E2 Rate Law (Bimolecular Elimination)★
$Rate = k [R-X] [Base]$
Concerted anti-periplanar removal of H and X. Follows Saytzeff's rule — more substituted alkene is major product.
4.E1 Rate Law
$Rate = k [R-X]$
Ionisation to carbocation (slow) then β-H loss (fast). Competes with SN1 in the same conditions.
5.SN2 Reactivity Order
$CH_{3} X > 1^{\circ} > 2^{\circ} > 3^{\circ} (primary allylic/benzylic > primary)$
Fewer alkyl groups on carbon ⇒ easier back-side attack. Bulky 3° halides are unreactive to SN2.
6.SN1 Reactivity Order
$3^{\circ} > 2^{\circ} > 1^{\circ} > CH_{3} X$
More alkyl groups stabilise the carbocation intermediate (hyperconjugation + inductive effect).
7.Finkelstein Reaction★
$R-Cl (or R-Br) + NaI acetone R-I + NaCl (or NaBr)$
Halide exchange in dry acetone. NaCl/NaBr precipitate out, driving equilibrium to R-I.
8.Swarts Reaction
$R-Br + AgF \to R-F + AgBr$
Preparation of alkyl fluoride from alkyl bromide/chloride using AgF, Hg₂F₂, CoF₂, or SbF₃.
9.Wurtz Reaction
$2 R-X + 2 Na dry ether R-R + 2 NaX$
Coupling of two alkyl halides via Na. Only works well for identical R groups (symmetric alkanes).
10.Wurtz-Fittig Reaction
$Ar-X + R-X + 2 Na dry ether Ar-R + 2 NaX$
Couples an aryl halide with an alkyl halide to give an alkylarene.
11.Sandmeyer Reaction★
$Ar-N_{2}^{+} X^{-} CuCl / CuBr Ar-Cl (or Ar-Br) + N_{2}$
Diazonium salt → aryl halide via Cu(I) halide. For Ar-I, KI alone works (no Cu needed).